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Description

Autonomy does not mean independence. It refers, rather,
to the capacity of a system to define its own rules of operation
as such a system, including the rules of interaction
with its environment. This applies to biological systems
which are able to build their boundaries (lipid membranes)
and other functional components (proteins, sugars, nucleic
acids, etc.) through the transformation of externally available
material and energetic resources. They manage to do
so by putting together and coordinating (both spatially
and temporally) a complex network of reaction processes
that take place in non-homogeneous, far-from-equilibrium
thermodynamic conditions. Thus, biological systems, being
necessarily open systems, constitute a dynamic organisation
of processes that becomes clearly distinct from the
inert environment that nurtures them and, at the same time,
collects the products of their ongoing activity.
In this article, I will argue that autonomy, in its most basic
and minimal sense, had to be developed quite early in the
sequence of transitions that led from complex physicalchemical
systems to the simplest biological ones. Apart
from relevant experimental evidence provided in present
days by several labs, a theoretical model will be introduced
to show how this could be achieved: namely, through the
coupling of autocatalytic chemical reaction networks
with processes of lipid self-assembly forming the membrane
of the system. This marks an important transition, in
which »vesicles« (closed bilayers) transform into »protocells
«, for they gain control on the production of their own
boundaries, a crucial step for autonomous individuation
and system-level regulation. The idea will be illustrated
both for protocells made with various types of lipidic molecules,
some of which are internally synthesized (Fig. 1),
and for more complex cases in which lipids are combined
with oligopeptides (Fig. 2), bringing about a richer space
of dynamic and regulatory behaviours.
Accordingly, lipid boundaries will not be portrayed as barriers,
as molecular structures that serve for separation or disconnection with the surrounding milieu but, rather, as
linkers of processes: i.e., as the organic interfaces in which
diverse mechanisms to control energy-matter flows are anchored,
making actually possible the continuous constructive
dynamics of biological systems. The complementary
relationship between boundaries and internal network of
reactions will be, therefore, highlighted, following the
steps of the autopoietic theory, but giving a more physically
grounded and updated interpretation of the idea.
Furthermore, autonomy will be claimed as a necessary
but not sufficient theoretical construct to account for living
phenomena, whose evolutionary-historical-collective
dimensions also need to be taken specifically into account.